The long-term goal of this research is to investigate the fetal origins of breast cancer and the role of environmental factors during early development, conception-weaning. 2 sources of estrogenic exposure relevant to man will be studied: a phytoestrogen preparation from soy mainly containing genistein and daidzein, and the ubiquitous environmental xenoestrogen 4-nonylphenol. Our hypothesis states the maternal estrogenic environment has a strong influence on risk to mammary tumorigenesis in adult life. 2 corollaries are: (a) phytoestrogens (90 ppm genistein/daidzein), in conjunction with an isocaloric 20% fat-diet having high n-3/n-6 polyunsaturated fatty acid balance, will significantly lower the risk of mammary tumors; and (b) xenoestrogen exposure (25 ppm 4-nonylphenol), in conjunction with a low dietary n-3/n-6 fatty acid balance, will promote the risk. The hypothesis will be tested in a unique mouse model for breast cancer having mammary-specific expression of a conditional mutation in the tumor suppressor Trp53 allele (flox'd p53.R270H/WAP-Cre model). The "humanized" mutant allele is permanently activated in the mammary gland epithelium exclusively in females traversing their first pregnancy-lactation cycle. This expression predisposes females to mammary tumors (-70% incidence) between ages 25-52 weeks. The project has 2 concurrent Specific Aims. (1) To investigate the effects of gestational-neonatal exposure to phyto/xenoestrogens on mammary gland development and tumorigenesis in female offspring heterozygous for the conditional p53.R270H allele reared on diets of low and high n-3/n-6 fatty acid composition. (2) Using the powerful combination of gene expression profiling with laser capture microdissection enumerate the molecular abundance profiles of epithelial end-buds and subtending ducts as foci for pre-malignant changes in the naive (virgin) and initiated (parous) mammary gland of p53.R270H/WAP-Cre females. These studies will provide new biomarker leads based in genetic regulatory networks that correlate (or anti-correlate) with altered fetal programming and pre-malignancy together with the realization of how such networks might relate functionally to the prenatal environmental risk factors in breast cancer.